Method of abrading a test track with a bituminous surface

ABSTRACT

A method for breaking in the surface condition of an asphalt test track for vehicles, comprising: modifying the condition of the surface of the test track with a treatment machine; placement on the treatment machine ( 1 ) of at least one rotary abrasive disc ( 4 ); and moving the treatment machine on the test track so as to reduce the friction coefficient to achieve a friction level corresponding to that of a broken-in track.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for breaking in the surfacecondition of a test track for vehicles, said track being of asphalt,comprising the provision of a treatment machine comprising a rotary headbearing at least one friction element for modifying the condition of thesurface of said test track, the placement on the treatment machine of atleast one rotary abrasive disc and the treatment of the surface to bemodified.

PRIOR ART

The manufacturers of road surfacings continually develop new products inorder to improve the quality of the roads. Generally, the aim is toincrease the durability of the surfacings as well as their mechanicalqualities in order to obtain a better vehicle road-holding. To this end,the aim is therefore most often to increase the friction coefficient ofthe surfacing.

For their part, the constructors and motor vehicle equipment suppliershave to be able to test their vehicles and components in the mostrealistic and repetitive conditions possible. In particular, with regardto the tyres, the European Union Regulations R117 and R228 specify, intheir Annex 5, the method for measuring the wet grip index of the tyres.This method provides notably for the average maximum braking forcecoefficient of a test tyre to be within specific ranges of values. Somestandards thus provide friction coefficient values for the surfacings ofthe tracks on which the tests are carried out.

Because of the ever improving qualities of the new surfacings on the onehand, and the objectives of performing tests representative of roadconditions on older surfacings, the newly constructed test tracks maynot respect certain requirements with respect to the frictioncoefficient. Various approaches have therefore been tried in order totreat the surface of the new surfacings of the tracks in order to makethem rapidly conform, at acceptable costs. The known methods areessentially based on the following principle: rubbing a rubber pad withor without abrasive particles to obtain the ground wear.

Given the large surfaces to be treated, the method has to be simple,effective and adaptable to long tracks. Currently, no truly conclusivemethod is available.

The polishing machines are also well known. For example, the documentUS20070272223 describes a polishing machine comprising a rotary frictionsurface provided with bristles. These bristles can be covered withabrasive particles such as silicon carbide for example. This type ofmachine is used for example to polish concrete grounds.

The document WO2005113198 illustrates an example of a polishing brushcomprising bristles encrusted with metal abrasive particles. Theseabrasive bristles are for example used in order to polish concretegrounds.

There is still a need to establish a method that makes it possible tobreak in a new test track of which the friction coefficient of thecoating does not make it possible to perform representative tests.

To mitigate these various drawbacks, the invention provides differenttechnical means.

SUMMARY OF THE INVENTION

The main objective of the invention consists in defining a surfacetreatment method that makes it possible to lower the level of grip of anew test track to bring it within a determined target, such as, forexample, a target provided by the current regulation.

To do this, the invention provides a method for breaking in the surfacecondition of an asphalt test track for vehicles, comprising thefollowing steps:

-   -   provision of a treatment machine comprising a rotary head        bearing at least one friction element, for modifying the        condition of the surface of said test track;    -   placement on the treatment machine of at least one rotary        abrasive disc;    -   application of movements of the treatment machine on the test        track so as to reduce the friction coefficient to achieve a        friction level corresponding to a target value.

This method makes it possible to modify the friction characteristics ofthe track in order to obtain a range of predetermined characteristics,for example specific wet grip characteristics.

It should be noted that this method has no significant influence on thedepth of the macrotextures (MTD, according to the standard EN13036-1)and consequently does not affect the drainage characteristics. Asdescribed later in this document, the other tests trialled all have anegative impact regarding this descriptor.

According to an advantageous embodiment, the method comprises apreliminary step of preparation consisting in eliminating the bituminousbinder on the surface of the aggregates by hydrostripping. Such a stepmakes it possible to obtain favourable results with shorterimplementation delays.

According to an advantageous embodiment, the friction element is anabrasive disc with bristles impregnated with abrasive particles.

The bristles advantageously have a height greater than 15 mm.

The form factor of the bristles is advantageously between 1/50 and 1/10,and more preferentially between 1/40 and 1/30.

For example, the height of the bristles is advantageously less than 60mm. The diameter of the bristles is advantageously between 2 and 4 mm.

Unexpectedly, this configuration makes it possible to obtainparticularly advantageous results. The tool used makes it possible toperform work over all the perimeter of the aggregates, and not onlytheir top surface.

Advantageously, the abrasive particles of the bristles are of siliconcarbide (SiC), ceramic or tungsten carbide type.

These particles, covering or embedded in the bristles or filaments, makeit possible to interact optimally with the aggregates of the surfacing.

According to an advantageous embodiment, the speed of rotation of therotary discs is between 1000 and 1500 revolutions/minute and morepreferentially substantially 1200 revolutions/minute.

According to another advantageous embodiment, the speed of movement ofthe machine is between 0.5 and 15 metres/minute and more preferentiallybetween 5 and 10 metres/minute.

The fact that the friction is generated by rotary discs makes itpossible to avoid giving the abrasion a directional aspect.

The number of passes of the machine is preferably between 1 and 10 andmore preferentially between 2 and 6.

Advantageously, the average contact pressure of the bristles of theabrasive discs is between 1 and 5 bar, preferably between 2 and 4 bar.

According to an advantageous embodiment, a working load of preferablybetween 200 and 400 kg and more preferentially between 260 and 300 kg isapplied to the treatment machine.

According to another advantageous embodiment, the machine comprises asensor giving an indication concerning the trend of the treatment, suchas, for example, a sensor of pendulum type (such as a “British PendulumTester” sensor). This configuration makes it possible to simply controlthe progress of the method.

The invention also provides a tyre test track surface treatment machinefor implementing the breaking-in method previously described, comprisinga rotary head bearing at least one friction element capable of modifyingthe condition of the surface of said test track, wherein the frictionelement is an abrasive disc with bristles impregnated with abrasiveparticles, and wherein the form factor of the bristles is advantageouslybetween 1/50 and 1/10, and more preferentially between 1/40 and 1/30.

DESCRIPTION OF THE FIGURES

All the details of realization are given in the following description,complemented by FIGS. 1 to 9, presented purely as nonlimiting examples,and in which:

FIG. 1 is a schematic representation of an example of a surfacetreatment machine;

FIG. 2 is a bottom view of the machine of FIG. 1, equipped with brusheswith abrasive bristles;

FIG. 3 is a schematic profile view of a brush with abrasive bristles;

FIG. 4 is a schematic representation in perspective of a filament ofwhich the brush with abrasive bristles is composed;

FIG. 5 is a bottom view of an example of an abrasive disc;

FIG. 6 is a schematic representation in profile view of a loadedcarriage in polishing position and provided with a pad;

FIG. 7 is a table illustrating the effects observed on the surfacing fordifferent types of polishings;

FIG. 8 is a table summarizing the types of tyres used for thecomparative tests;

FIG. 9 is a summary table of the variations in μ_(ASTM) obtained foreach of the tests carried out.

DETAILED DESCRIPTION OF THE INVENTION

As has been seen previously, the grip levels sought for the vehicleand/or tyre test tracks are for example defined in standards.

The method needs to be able to cover all the range of values0.5<μ_(ASTM-16pces)<0.9, and more preferentially the values0.6<μ_(ASTM-16pces)<0.8.

Various polishing techniques were tested on a track which was speciallyconstructed for this study. The various results obtained show that thebreaking-in technique using a resurfacer equipped with brushes withabrasive bristles of great height is most effective for achieving thetarget sought in terms of μ_(ASTM) level. The analyses have made itpossible to construct a two-fold demonstration:

i) on the one hand that the technique makes it possible to achieve atarget grip through the range previously cited;ii) the known tyre behaviour tests performed on a new track treated withthe method according to the invention made it possible to obtain tyreclassification results comparable to those previously obtained onregulatory or other test tracks.

Conclusive Characteristics

-   -   Rate of advance: 0.5 m/min;    -   Number of passes to be performed: ≥4;    -   μ lowering rate: 0.07 pt μ_(ASTM) per pass.

Track Used to Determine the Effective Criteria

A track of 550 m² was specially constructed in an area of low activityof a tyre test centre. It consists of two different surfacings (Sol1 andSol2) taken from wet braking tracks. After preparatory work whichconsisted in eliminating the bituminous binder from the surface of theaggregates by hydrostripping and delimiting the working zones, the trackwas handed over to test polishing methods.

The choice of road surfacings is geared towards the following solution:

-   -   Sol1: track with low microroughness and open macroroughness        favouring water evacuation; surface of 5×60 m²;    -   Sol2: track with high microroughness and closed macroroughness;        surface of 5×50 m².

Tests Carried Out

Several distinct approaches were tested, according to two test families:

A1) pad with high load (high pressure);A2) pad with low load with SiC (low pressure);B1) sanding machine with tyre tread;B2) sanding machine with abrasive discs;B3) sanding machine with rotary brushes equipped with bristlesimpregnated with abrasive particles.Pad with High Load (High Pressure)

A pad of large dimension comprising a bottom friction surface providedwith a plurality of tyre treads arranged in parallel, serves as aworking surface. To improve the effectiveness, loads are placed on thepad. The pad forms a kind of trailer without wheels, pulled by a tractoror other vehicle of high traction power. FIG. 6 schematicallyillustrates an example of a pad on which loads are placed.

The idea behind the HP pad technique is therefore to create a devicewhich makes it possible to cause the rubber to rub on the surfacing tobe broken in with the right pressure and for long enough.

The study began with the production of a specific carriage. The carriageconsists of a robust metal frame, which can be manipulated by a“standard” tractor (for lifting and transportation) and placed on rubberpads. For the pressure exerted, the carriage weighs in all 2200 kg. Thecarriage rests on 4 pads of 6.5×24.0 cm²=637 cm²; the contactpressure=3.4 bar.

The implementation of the HP pad gave rise to a certain number ofincidents. The sprinkling system had to be modified to reduce the riskof destruction through burning. The pads were wearing out very quickly.Then, shims had to be added to extend the life of the pads. All thatcombined with a fairly uncomfortable working posture for the operator,who had to spend his or her time watching behind him or her. The resultof that was that productivity was very mediocre. An average of elevenpasses per day were completed during the tests.

The implementation made it possible to rapidly identify two defects onthe first batch of pads which were manufactured: stripping bydelamellization; wear by burning.

t can be estimated that the necessary number of passes needs to be ofthe order of 2000 to achieve the asymptote of the different grounds. Itis also probable that the number of passes should be dependent on theground treated. It must be stressed that the implementation of the HPpad technique brings a working situation that is particularly difficultfor the operator, making the solution difficult to industrialize.

Pad with Low Load with SiC (Low Pressure)

This approach is comparable to the preceding one for the main support,namely the pad. It is however used without load placed on the pad. Toreplace the load, an intermediate material is used, acting between thepad and the ground. The test therefore involves arranging a layer of SiCon the ground before performing the passes with the pad.

The technique works at an average contact pressure that is extremely lowP=0.03 bar. The surface is approximately 4 m² and the weight is of theorder of 250 kg.

The use of powder needs to respect the conventional polishingtechniques. We start with a large particle size and end with a fineparticle size. For these tests, three particle sizes had been procured:10, 5 and 3 μm. After treatment, cleaning the treated zone was not easy.

Looked at from the viewpoint of the aggregate used in the surfacing, theslipped length is significantly greater than the HP pad technique. Oneach pass, an aggregate undergoes 2 m of slipped length.

It can be reported that the technique was not effective. From theviewpoint of the μ_(ASTM) friction coefficient and regardless of theground watched, the technique does not give a result. This is probablylinked to the indentation phenomenon. The LP pad+SiC technique worksessentially on the surface of the aggregate, and the tyre, for its part,touches unworked zones. As a first approximation, it is thought thatthere would need to be approximately 5000 passes to manage to bring thep level to the expected target. The technique is highly polluting. Oncethe polishing work is finished, the elimination of the SiC is relativelydifficult.

Sanding Machine

The machine is electrical and requires a standalone set to power it asfar as the track.

An example of sanding treatment machine 1 and of its different elementsis illustrated schematically in FIGS. 1 to 4. In the exampleillustrated, the machine 1 has a rotary head 2 and is mounted on wheels8. The rotary head comprises three friction elements 3 (4=220 mm). Eachof the friction elements 3 is rotated about its central axis. The speedis adjusted by variable speed drive to a rotation speed of 1200 rpm. Thefriction elements 3 comprise brushes 4 provided with bristles 5. Asillustrated in FIG. 4, at least a portion of the bristles 5 is coatedwith abrasive particles 6. The set of the three brushes 4 is rotatedabout the central axis 7 of the machine (of the order of 100 rpm), thusgenerating a double rotation movement of the abrasive discs 4.

The abrasive particles 6 are advantageously composed of SiC, of ceramicsor of tungsten carbide.

The machine used in the tests has an autonomous driving system withadjustable speed. The machine is piloted by an operator byradiocommunication. The operator has to be situated within a perimeterof 5 m around the machine. Other operating parameters are adjustable:the deballasting weight and the sprinkling. As is known, the devicepresented is used for brightening or cleaning tasks. In these cases, thebristles do NOT include abrasive particles.

The implementation requires the availability of an electrical generatorset. The time required to assemble the equipment is relatively short butnecessitates lifting equipment to rapidly transport the machine. Duringuse, a continuous sprinkling is necessary. It makes it possible todischarge sludge and ensures the cooling of the interface and of theground. One or more loads 9 or weights can be applied to the machine inorder to increase the effectiveness of the polishing.

The tests were performed with a “Blastrac” model 780RS polishingmachine.

Sanding Machine with Discs with Tyre Tread

For this test, the abrasive discs 4 are composed of portions of tyretread. The diameter of the discs used was 220 mm. The height of thetread was 8 mm.

The tests were very quickly stopped. The join between the pad and themachine was not sufficiently strong and the discs were torn away.

Sanding Machine with Grain Abrasive Discs

FIG. 5 schematically illustrates an example of a grain abrasive discused for this test. These discs are composed of a resin in which“grains” of tungsten carbide are integrated. Depending on the densityand the particle size of these grains, the degree of abrasiveness iscontrolled.

Sanding Machine Using Brushes Comprising Bristles Encrusted withParticles (SiC)

FIGS. 2, 3 and 4 (previously described) illustrate an example of adevice for these tests.

The tests were done with a fixed rate of advance of the order of 0.5m/min. Additional tests were carried out at a speed of 10 m/min. Adouble rotation is advantageously used. The pressure is situated between0.2 and 0.3 bar.

This test configuration made it possible to achieve the target sought interms of p level. Moreover, comparative tests with tyres of knownrelative grip performance levels on one of the treated zones deliveredresults identical to those obtained on the “conventional” tracks (FIG.8).

From an effectiveness point of view, the technique based on a brush withabrasive bristles of great height is the most effective for lowering theμASTM.

Main Results

The many technical difficulties to be overcome to create the prototypes,perform the tests in good conditions of safety, monitor the effectsobtained, then compare with prior results providing a guarantee of theauthenticity of the observed effects, shows that developing abreaking-in method is a particularly complex and lengthy process, theresults of which are totally unpredictable.

FIG. 7 schematically illustrates the main effects produced on thesurfacing with the methods tested. The first illustration represents theprofile of the surfacing prior to breaking-in. The aggregates or pebblesform a rough surface. The next two illustrations show the particularlylimited effect of the pads (pad+SiC and HP pad). The last illustrationshows the effect of the abrasive disc, working only on the surface.Finally, the penultimate illustration presents the effect obtained withbrushes whose filaments comprise abrasive particles in their mass (SiCfor the tests carried out). It is observed that the bristles make itpossible to reach all the reliefs, on the top and on the sides, for aparticularly conclusive three-dimensional effect with respect to thetargeted aim of reducing the friction coefficient.

FIG. 9 shows the friction coefficient values obtained. The advantageousresults from the brush with abrasive bristles of great height describedpreviously are confirmed.

This table makes it possible to draw many conclusions:

-   -   the threshold of 0.7 μ_(ASTM) was achieved by just one of the        techniques implemented: the brush with bristles encrusted with        particles of silicon carbide (SiC);    -   the LP carriage+SiC did not have any effect from the μ_(ASTM)        point of view;    -   the grain 2000 sanding machine did not have any effect;    -   the tests with a brush with abrasive bristles of great height        make it possible to achieve the target 0.6<μ_(ASTM)<0.8 (that        confirms the robustness of the technique);    -   the reference plot shows a μ_(ASTM) of the order of 1. The        measurement dispersion is of the order of 0.1 point;    -   the HP pad presents a fairly slow polishing kinetic, the trend        goes in the right direction but remains inadequate;    -   the grain 500 sanding machine is more effective than the grain        2000 but achieves an asymptote fairly far from the final target.

REFERENCE NUMBERS EMPLOYED IN THE FIGURES

-   1 Surface treatment machine-   2 Rotary head-   3 Friction element-   4 Abrasive disc or brush-   5 Bristles-   6 Abrasive particles-   7 Rotation centre-   8 Wheels-   9 Load

1.-14. (canceled)
 15. A method for breaking in a surface condition of anasphalt test track for vehicles, comprising: (a) modifying the surfacecondition of the test track with a treatment machine comprising a rotaryhead bearing at least one friction element; and (b) moving the treatmentmachine on the test track to reduce a friction coefficient to achieve afriction level corresponding to a target value, wherein the at least onefriction element is an abrasive disc.
 16. The method according to claim15 further comprising the step of hydrostripping the test track beforestep (a) to eliminate a bituminous binder on a surface of aggregates.17. The method according to claim 15, wherein the abrasive disccomprises bristles impregnated with abrasive particles.
 18. The methodaccording to claim 17, wherein the bristles have a height greater than15 mm.
 19. The method according to claim 17, wherein a form factor ofthe bristles is between 1/50 and 1/10.
 20. The method according to claim17, wherein the abrasive particles are selected from the groupconsisting of silicon carbide (SiC), ceramic and tungsten carbide type.21. The method according to claim 15, wherein a speed of rotation of theabrasive disc is between 1000 and 1500 revolutions/minute.
 22. Themethod according to claim 21, wherein the speed of rotation of theabrasive disc is about 1200 revolutions/minute.
 23. The method accordingto claim 15, wherein a speed of movement of the treatment machine isbetween 0.5 and 12 meters/minute.
 24. The method according to claim 23,wherein the speed of movement of the treatment machine is between 1.5and 5 meters/minute.
 25. The method according to claim 24, wherein thespeed of movement of the treatment machine is about 2 meters/minute. 26.The method according to claim 15, wherein a number of passes of thetreatment machine on the test track is between 1 and
 10. 27. The methodaccording to claim 26, wherein the number of passes of the treatmentmachine on the test track is between 2 and
 6. 28. The method accordingto claim 15, wherein a working load applied to the treatment machine isbetween 200 and 400 kg.
 29. The method according to claim 28, whereinthe working load applied to the treatment machine is between 260 and 300kg.
 30. A treatment machine for breaking in a surface condition of anasphalt test track for vehicles, comprising a rotary head bearing atleast one friction element capable of modifying the surface condition ofthe test track, wherein the friction element is an abrasive disc withbristles impregnated with abrasive particles, and wherein a form factorof the bristles is between 1/50 and 1/10.
 31. The treatment machineaccording to claim 30, wherein the abrasive particles are selected fromthe group consisting of silicon carbide (SiC), ceramic and tungstencarbide type.
 32. The treatment machine according to claim 30, whereinthe bristles have a height greater than 15 mm.
 33. The treatment machineaccording to claim 30, wherein an average contact pressure of thebristles is between 1 and 5 bar.
 34. The treatment machine according toclaim 33, wherein the average contact pressure of the bristles isbetween 2 and 4 bar.